In this study of low-cycle fatigue, the following steels were evaluated: (1) two reference steels used in pressure vessel construction, A 543, Grade B (200 mm thickness) and St 52-3 (50 mm thickness); these steels were also studied after heat treatments simulating heat-affected zones of weldments with heat inputs ranging from 10 to 150 kJ/cm; (2) one structural steel, St E47 (50 mm thickness), after either normalization or quench-tempering treatment in order to compare two characteristic values of the yield strength/ultimate tensile strength ratio; and (3) fifteen experimental steels (28 mm thickness) in a thermal condition simulating the water quenching at the core of a plate 200 mm thick, this quenching being followed by a tempering.

Smooth and notched specimens were fatigue tested at 20 and 350°C under completely reversed tension-compression. The imposed diametral strain range was controlled to a constant value throughout each test.

Results were compared with ASME design curves and showed sufficient performances in all cases, so that the choice of the steel may be based upon another use property or economical argument. Nevertheless, differences between steel fatigue properties were studied by statistical methods as a function either of the tensile properties or of the chemical composition in the case of quenched and tempered steels. Concerning these last correlations, the influence of chromium at 350°C was particularly noted.